The present invention concerns a system for the control of the quality of a laser cut or perforation, in particular for sheets of metal, by perforation herein essentially meaning the formation of the initial hole in preparation of the sheet metal cutting.
More precisely the present invention refers to systems for the verification of the absence of burr in the case of a laser cut and of the executed perforation or breaking of the sheet metal in the case of a laser perforation, and even more precisely to a system of the type comprising:
means to focus a laser beam onto a cut or perforation zone.
photodiode sensor means to detect the radiation emitted by the cut or perforation zone, and an electronic control and processing unit to process the signals emitted by said sensor means.
Systems of the aforementioned type have already been proposed and used in the past to carry out an on-line monitoring of the laser cutting process of the sheet metal, and this with the aim of estimating the presence or absence of burrs in the cut zone.
The inconvenience with the systems used so far resides in the fact that they base the control of the quality on a comparison between the signals that are detected during the cutting process and one or more predetermined reference signals indicative of a good quality cut, that is in the absence of burr. Such reference signals, usually in a number varying from two to ten, are predisposed starting from several good quality cut specimens. Obviously, this way to proceed implies the presence of an expert operator who is capable to certify the soundness of the cut at the moment of the creation of the reference signals, it involves expenditure of time and sometimes even waste of material (that gets wasted in order to produce the specimens necessary to obtain the reference signals). In some cases reference signals indicative of a cut with defects, that is with presence of burr, are also provided which involves additional problems and difficulty.
The main scope of the present invention is to provide a system for the control of the quality of a laser cut, that allows to overcome all the aforesaid disadvantages.
Another scope is to provide a system for the control of the quality that is usable also to verify the executed perforation or breaking in a process of perforation of the sheet metal.
In order to attain such scopes, the invention has as an object a system for the control of the quality of a laser cut or perforation having the characteristics indicated at the beginning and characterised also in that an optical filter is associated with the aforesaid photodiode sensor means that is suitable to select an optical band around 620 nm, in that said control and processing means are suitable to acquire the signal coming from said sensor means with a frequency comprised between 10 and 60 kHz and in that said control and acquisition means are suitable to filter the acquired signal with the aid of a band-pass filter between 7 and 16 kHz, in such way so that the control of the quality of the cut or the perforation can be carried out on a basis of the sole signals thus processed, without the need of a comparison with predetermined reference signals corresponding to a good quality cut or perforation.
In the preferred embodiment, the aforesaid control and processing means are suitable to divide the acquired and filtered signal into blocks, to make an average of the signal for each block being sampled and to identify the presence of a defect in the cut or perforation in the case in which such blocks shows a value higher than the offset of the sensor means.
Past experiences by the applicant have shown that, owing to the aforesaid characteristics, the simple analysis of the signals detected during the cut or perforation process is therefore sufficient to allow the identification of possible defects, without any need to predispose reference signals indicative of a good quality cut or perforation and therefore with the advantage to eliminate the relatively laborious operations for the predisposition of reference signals.
Naturally, the invention has also for an object the procedure for the control of the quality of a laser cut or perforation that utilises the above described system.
Additional characteristics and advantages of the invention will become evident from the following description with reference to the enclosed drawings, that are provided as a purely non-limiting example, in which: